Conventionally, there is an optical disk drive which irradiates an optical disk rotating at a predetermined rpm with a light beam emitted from a light source such as a semiconductor laser or the like to reproduce a signal recorded on the optical disk. Hereinafter, an optical disk drive according to a first prior art will be described with reference to FIGS. 8 and 9.
In FIG. 8, a disk 100 is fixed to a rotation axis 102 of a motor 101, and rotates at a predetermined rpm.
The disk 100 has spiral tracks on which pits and projections are formed, and data are recorded on the tracks, i.e., the pits and projections. The track pitch is 0.74 micrometer (hereinafter referred to as “μm”), and the width of each pit and projection is about 0.6 μm.
A laser 109 as a light source, a coupling lens 108, a polarization beam splitter 110, a ¼ wavelength plate 107, a total reflection mirror 105, a photodetector 113, a detection lens 111, a cylindrical lens 112, and an actuator 104 are fixed onto a carrier 115 of an optical pickup, and the carrier 115 is driven by a motor 114 in the direction of the radius of the disk 100.
A laser driving circuit 175 drives the laser 109 according to a command from a DSP 140. The laser 109 is fixed onto the carrier 115. A light beam 106 emitted from the laser 109 is converted into a parallel light beam by the coupling lens 108, travels through the polarization beam splitter 110 and the ¼ wavelength plate 107, is reflected at the total reflection mirror 105, and is focused on an information surface of the disk 100 by a convergence lens 103.
The light beam reflected at the information surface of the disk 100 travels through the convergence lens 103, and is reflected at the total reflection mirror 105. The reflected light beam travels through the ¼ wavelength plate 107, the polarization beam splitter 110, the detection lens 111, and the cylindrical lens 112, and enters into the photodetector 113 comprising four photoreceptive parts.
The convergence lens 103 is fixed to a movable part of the actuator 104. The actuator 104 is composed of a focusing coil, a tracking coil, a focusing permanent magnet, and a tracking permanent magnet.
When a voltage is applied to the focusing coil (not shown) of the actuator 104 by using a power amplifier 152, a current flows in the coil, and the coil receives a magnetic power from the focusing permanent magnet (not shown), whereby the convergence lens 103 moves in the direction perpendicular to the information surface of the disk 100 (vertical direction in FIG. 8). The convergence lens 103 is controlled so that the focal point of the light beam 106 is always positioned (focused) on the information surface of the disk 100, on the basis of a focusing error signal indicating a deviation of the focal point of the light beam from the information surface of the disk.
Further, when a voltage is applied to the tracking coil (not shown) using a power amplifier 145, a current flows in the coil, and the coil receives a magnetic power from the tracking permanent magnet (not shown), whereby the convergence lens 103 moves in the direction of the radius of the disk 100, i.e., across the tracks on the disk 100 (horizontal direction in FIG. 8).
The photodetector 113 is composed of four photoreceptive elements. The reflected light beam from the disk is incident on the photodetector 113. In the photodetector 113, the incident light beam is converted into currents by the four photoreceptive elements, and the currents are sent to I/V converters 116, 117, 118, and 119. Each of the I/V converters 116, 117, 118, and 119 converts the inputted current into a voltage according to the current level.
Each of adders 120, 121, 123, 124, and 130 performs addition of input signals, and outputs the sum. Each of subtracters (hereinafter also referred to as differential circuits) 122 and 125 performs subtraction of input signals, and outputs the difference.
To be specific, the adder 124 adds the outputs of the I/V converters 116 and 117, the adder 123 adds the outputs of the I/V converters 118 and 119, the adder 120 adds the outputs of the I/V converters 116 and 119, the adder 121 adds the outputs of the I/V converters 117 and 118, and the adder 130 adds the outputs of the adders 124 and 123. The subtracter 125 subtracts the output of the adder 123 from the output of the adder 124. The subtracter 122 subtracts the output of the adder 121 from the output of the adder 120.
The output from the subtracter 122 is a focusing error signal which indicates a deviation of the focal point of the light beam applied to the disk, from the information surface of the disk 100. The focusing error signal is transferred to an analog-to-digital converter (hereinafter referred to as an A/D converter) 149, and processed through a phase compensation circuit 150, a digital-to-analog converter (hereinafter referred to as an D/A converter) 151, and a power amplifier 152, whereby a current flows in the focusing coil of the actuator 104.
The A/D converter 149 converts an analog signal into a digital signal. Further, the D/A converter 151 converts a digital signal into an analog signal.
The phase compensation circuit 150 is a digital filter, and performs phase compensation on the focusing servo system to stabilize the servo loop. In this way, the convergence lens 103 is driven according to the focusing error signal, and the focal point of the light beam is always positioned (focused) on the information surface of the disk.
The optical system shown in FIG. 8 constitutes a method of detecting a tracking error signal (hereinafter referred to as a TE signal), which is generally called a push-pull method. Accordingly, the output from the subtracter 125 becomes a TE signal which indicates a deviation of a spot of the light beam applied to the optical disk from a track on the disk 100. Hereinafter, the output from the subtracter 125 is referred to as a first TE signal. The first TE signal is transferred to a switch 155, and processed through an A/D converter 143, an adder 142, a phase compensation circuit 144, a D/A converter 170, and the power amplifier 145, whereby a current flows in the tracking coil of the actuator 104.
The phase compensation circuit 144 is a digital filter, and performs phase compensation on the tracking servo system to stabilize the servo loop. Accordingly, the convergence lens 103 is driven according to the first TE signal, whereby the spot of the light beam always follows the tracks.
Further, the TE signal is transferred to a power amplifier 129 through a low-pass filter 146, a D/A converter 147, and an adder 148. Since the carrier motor 114 is driven by the power amplifier 129, the carrier motor 114 is controlled according to the low-frequency component of the TE signal. That is, in the tracking servo system, tracking is carried out by the actuator 104 for a response of high frequency, and tracking is carried out by the carrier motor 114 for a response of low frequency.
Next, the adder 130 adds the outputs of the adders 123 and 124. That is, the output from the adder 130 is the total amount of light received by the photodetector 113. Hereinafter, the output signal from the adder 130 is referred to as a total reflected light amount signal. The output from the adder 130 is transferred to an address reproduction circuit 131. The address reproduction circuit 131 reproduces a sector address, and sends it to a digital signal processor (hereinafter referred to as a DSP) 140. Further, the address reproduction circuit 131 outputs a signal synchronized with the address to a gate generation circuit 132.
The gate generation circuit 132 outputs, to a switch 133, a gate signal which becomes high level in VFO1 and VFO2 areas of the address section. Hereinafter, signals in the VFO1 area and the VFO2 area are referred to as a VFO1 signal and a VFO2 signal, respectively. Further, as shown in FIG. 9, the gate generation circuit 132 generates a sampling signal for sampling and holding the VFO1 signal and the VFO2 signal which are extracted by the gate signal that becomes high in the VFO1 and VFO2 areas of the address section, respectively. The sampling signal generated in the gate generation circuit 132 is outputted toward a sample hold circuit (hereinafter referred to as an S/H circuit) 136 for sampling the VFO1 signal in the address section, and it is also outputted toward an S/H circuit 137 for sampling the VFO2 signal in the address section.
The switch 133, an HPF 172, a full wave rectifier 134, an LPF 135, S/H circuits 136 and 137, and a subtracter 138 constitute a circuit for detecting a second TE signal. The output from the subtracter 138 is the second TE signal.
The second TE signal is transferred through a switch 153, converted into a digital signal in an A/D converter 152, and transferred to the adder 142.
Next, the operation of the DSP 140 when the tracking servo is operated will be described.
In the initial state, the DSP 140 closes the switch 155 while the switch 153 is open, thereby operating the tracking servo. Therefore, the convergence lens 104 is driven on the basis of the first TE signal.
The address reproduction circuit 131 reads an address at a position irradiated with a beam spot, on the basis of the output from the adder 130, i.e., the total reflected light amount signal, and sends an address signal to the DSP 140. The DSP 140 identifies a zone on the optical disk on the basis of the address. Then, the DSP 140 sends a command to a motor control circuit 171 so that the rpm of the disk 100 reaches an rpm according to the zone. When the rpm of the disk 100 reaches the predetermined rpm, the address reproduction circuit 131 sends a signal synchronized with the address, to the gate generation circuit 132.
The gate generation circuit 132 generates an address signal, a VFO1 signal, and a VFO2 signal, and outputs these signals as control signals to the switch 133, the sample hold circuit 136, and the sample hold circuit 137, whereby a second TE generation circuit 200 outputs a second TE signal from the output of the subtracter 138.
Next, the DSP 140 corrects the target position of the tracking servo system which is operating on the basis of the first TE signal. That is, in the adder 142, the second TE signal is added to the tracking servo system based on the first TE signal, thereby adding an offset to the tracking servo system. Since plural tracks are formed in a spiral on the disk, and the track pitch is 0.74 μm. A recording film comprising a phase changing material or the like is formed on the information surface of the disk. When recording data on the disk, the reflectivity of the recording film is changed by changing the intensity of the light beam according to the data while performing tracking servo so that the light beam is always focused on the track. When reproducing data from the disk, the reflected light beam from the optical disk is received by the photodetector while performing tracking servo so that the light beam is always focused on the track, and the output from the photodetector is processed to reproduce the data.
The amount of deviation of the light beam from the track, which is required for tracking servo, is also detected from the reflected light from the disk. Hereinafter, a description will be given of a tracking error detection method which is generally called a push-pull method.
The push-pull method is also called a far field method. In this method, a light beam which is reflected and diffracted at a guide groove on the disk is applied to two photoreceptive elements of a two-part photodetector, which are arranged symmetrically with respect to the center of track, and a difference of the outputs from the photoreceptive elements is taken out as a TE signal. As shown in FIG. 10(b), when the spot of the light beam is aligned with the center of the projection or pit of the groove, a symmetrical distribution of reflected and diffracted light is obtained. However, in other cases (FIGS. 10(a) and 10(c)), the light intensity becomes asymmetrical. FIG. 11 shows a difference in outputs from the two-part photodetector when the spot of the light beam travels across the tracks. The TE signal becomes 0 in the center of the pit or projection. Tracking servo is carried out as follows. The tracking actuator is driven through the phase compensation circuit and the driving circuit according to the TE signal, and the spot on the disk is driven in the direction perpendicular to the tracks to follow the target track.
Next, a description will be given of an optical disk drive according to a second prior art, with reference to FIG. 12.
Since the fundamental control operations such as focusing servo and tracking servo are identical to those described for the first prior art, repeated description is not necessary.
A digital control circuit for an optical disk drive is divided into an analog signal processing integrated circuit and a digital signal processing integrated circuit in many cases. Hereinafter, an integrated circuit is referred to as an IC.
In FIG. 12, IC1 denotes an analog signal processing IC, and IC3 denotes a digital signal processing IC.
The analog signal processing IC IC1 is supplied with signals, which are obtained by I/V converting the light beam reflected at the disk and incident on the photodetector 113, by the I/V converters 116, 117, 118, and 119.
Each of adders 120, 121, 123, 124, and 130 performs addition of input signals, and outputs the sum. Each of subtracters (differential circuits) 122, 125, and 126 performs subtraction of input signals, and outputs the difference.
The output from the subtracter 122 is outputted from the analog signal processing IC IC1 as a focusing error signal which indicates a deviation of the focal point of the light beam applied to the disk, from the information surface of the disk. Further, the output from the subtracter 125 is a first TE signal based on the push-pull method for making the spot on the disk follow the target track. The first TE signal based on the push-pull method is inputted to a switch 154, together with a TE signal based on the phase difference method, which is generated by a phase difference detection circuit 160. The switch 154 selects either the first TE signal based on the push-pull method or the TE signal based on the phase difference method, and outputs the selected signal as an output of the analog signal processing IC.
The total reflected light amount signal outputted from the adder 130 is supplied to a tilt detection circuit 161, a second TE generation circuit 162, and an RF amplitude detection circuit 163 in the analog signal processing IC IC1, and further, it bypasses the analog signal processing IC IC1 to be supplied to the digital signal processing IC IC3.
The tilt detection circuit 161 detects an angle formed between the disk and the light beam applied to the disk, and outputs the result of the detection to the digital signal processing IC IC3. The second TE signal generation circuit 162 corrects the target value of the first TE signal as described above, and outputs the result of the correction to the digital signal processing IC IC3. The RF amplitude detection circuit 163 detects the amplitude of a reproduced RF signal obtained from the total reflected light amount. The RF amplitude detection circuit 163 is used for detection as to whether a recording area on the disk has already been recorded or not, and detection of the RF signal amplitude. A switch 165 selects either the output from the RF amplitude detection circuit 163 or a wobble amplitude signal outputted from a wobble signal detection circuit 164, and outputs the selected signal to the digital signal processing IC IC3.
A wobble signal appears in the TE signal when the tracking servo follows a single track, because the tracks (pits and projections) formed on the disk wind at a high frequency. Since the wobble signal has a frequency ten times or more as high as the band frequency required for tracking servo, a broad-band subtracter is needed, and the subtracter 126 corresponds to the broad-band subtracter. In order to detect the amplitude of the wobble signal, the wobble signal which is included in the broad-band TE signal outputted from the subtracter 126 is inputted to the wobble signal detection circuit 164.
Further, the actuator (104 in FIG. 8) is provided with a position detector in the tracking direction. This position detector is used for suppressing a vibration of the actuator in the tracking direction when only the carrier is moved with the tracking servo being turned off, during search for the target track. A signal outputted from the position detector is amplified in a position detection circuit 166 and, further, it is differentiated in the position detection circuit 166. A switch 167 selects either the amplified signal or the differentiated signal, and outputs the selected signal to the digital signal processing IC IC3.
On the other hand, in the digital signal processing IC IC3, all of the output signals from the analog signal processing IC IC1 are inputted to a switch 168. The switch 168 successively selects the output signals according to A/D conversion commands from the DSP 140, and the selected signals are converted into digital signals by an A/D converter 169. The respective signals captured as digital signals are subjected to processing such as phase compensation by the DSP 140, and converted into analog signals by D/A converters 151, 170, and 147. These analog signals drive the actuator or the like through a power amplifier (not shown).
By the way, optical disk drives in recent years are constructed such that a single drive can deal with plural kinds of disks. For example, a DVD-RAM/ROM disk recording/playback device is adaptable to DVD-R recording, a DVD-ROM disk playback device is adaptable to CD-R/RW recording, and so on. In this case, an IC adapted to a disk to be newly handled is added to an IC adapted to a fundamental disk.
Hereinafter, an optical disk drive according to a third prior art, which is adaptable to plural kinds of disks, will be described with reference to FIG. 13.
Since the fundamental servo operations such as focusing servo and tracking servo are identical to those described for the first prior art, repeated description is not necessary.
In FIG. 13, IC1 is an analog signal processing IC adaptable to a fundamental disk such as a DVD-RAM/ROM or the like, IC2 is an analog signal processing IC which is added to deal with a new disk such as a DVD-R or the like, and IC3 is a digital signal processing IC adaptable to both of the fundamental disk and the new disk.
In this third prior art, as in the second prior art, the reflected signal from the disk, which is supplied from the photoreceptive element, is processed by a processing circuit 180, whereby various kinds of signals are outputted. Likewise, the reflected signal is supplied from a photoreceptive element which is provided for the new disk, and processed by a processing circuit 181, whereby various kinds of signals are outputted. The digital signal processing IC IC2 selects, by a switch 156, either the signals outputted from the analog signal processing IC IC1 or the signals outputted from the analog signal processing IC IC2 by using the switch 156, thereby deciding, for each disk to deal with, that the disk should be controlling by the outputs from the analog signal processing IC IC1 or the outputs from the analog signal processing IC IC2.
As described above, when a single optical disk drive is adapted to plural kinds of disks, the circuit components are increased, and the number of signal lines connecting the respective ICs is increased, whereby the number of pins of each IC is increased, resulting in disadvantages in cost and reliability.
As described above, since the recent optical disk drive is required to deal with plural kinds of disks, the circuit components are increased, and usually, an IC adapted to an additional disk is added to a fundamental IC structure. Accordingly, the number of connection lines tends to increase over the existing connection lines, and the above-mentioned problems are not fundamentally resolved unless the individual ICs corresponding to the respective disks are integrated into one.
Furthermore, when an additional IC structure is added to the fundamental IC structure, the number of connection lines between the ICs is increased, whereby the number of pins of each IC is increased, resulting in disadvantages in cost and reliability.